Surficial Geology and Soils of Southern Madison County, New York

Surficial Geology and Soils of Southern Madison County, New York Bruce W. Selleck, Colgate University, Hamilton, New York Introduction and General Bedrock Geology: Southern Madison County, New York lies south of the Onondaga-Helderberg Escarpment on the northern limits of the Appalachian Plateau. Local relief is approximately 600 feet, with valley floor elevations of 1100 feet in the vicinity of Hamilton, New York. The region is underlain by middle Devonian shales, siltstones and sandstones of the Hamilton Group. These fossiliferous rocks are rather poorly resistant to erosion, and surface outcrops are rare except in stream valleys and along steeply-sloping valley walls. One prominent sandstone unit in the Hamilton Group, the Chenango Sandstone, was quarried in the area as dimension stone. The older buildings on the Colgate University campus are built of Chenango Sandstone quarried on the hill south of the main campus. Progressively older Paleozoic rock units are exposed to the north, including lower and middle Devonian limestones of the Onondaga and Helderberg Groups, the lower Devonian Oriskany Sandstone, shales, sandstones and dolostones of Silurian age, upper Ordovician shales, and lower and middle Ordovician limestones. Upper Cambrian sandstones and dolostone overly Proterozoic basement rocks in the Mohawk Valley. Lithologies representing all of these rock units can be found within the glacial drift which mantles the bedrock of southern Madison County. The dominant exotic (lithologies other than Hamilton Group) rock types in the drift are limestone, dolostone, chert, sandstone and various Proterozoic rocks of Adirondack origin. Glaciation and Deglaciation: Pleistocene continental glaciation profoundly affected the topography and surficial geology of the area. Pre-glacial topography, dominated by generally north-south dendritic valley systems, was altered by enlargement and reshaping of valley cross-sections, and sculpting of upland bedrock surfaces. Although no direct evidence of pre-Wisconsin glaciation is observable in the area, it is assumed that multiple advance-retreat cycles occurred. The presence of reworked clasts of cemented glacial gravels in Wisconsin-age drift may imply the presence of pre-Wisconsin glacial deposits. However, such clasts may have been generated within relatively short time periods during the last deglaciation. Four phases within the deglaciation history can be identified: 1. Upland ice phase - No upland areas are know to have escaped glacial coverage during the Wisconsin maximum advance. Upland lodgement tills are often the only glacial deposits on upland ridges. In this region, the onset of deglaciation was characterized by thinning of the ice sheet to expose upland regions while active ice tongues occupied progressively lower elevation of the valleys. 251 2. Valley ice tongue phase- Active ice flow in the valleys is documented by the presence of glacial trim lines on valley walls, and deposition of ice-contact drift on valley margins. Kame terrace landforms characterize the valley walls in the region, and multiple terraces may indicate progressive lowering of the active ice surface within the valleys. 3. Fluvio-glacial outwash and stagnant ice phase - As the active ice margin retreated to a position near the present Onondaga Helderberg Escarpment, a complex period of minor advance and retreat of the ice sheet culminated with development of morainal deposits within the northern terminus of the major north-south valleys of the Appalachian Plateau. These deposits represent the so-called Valley Heads Moraine. In Madison County, these ice-margins fed major glacial streams which deposited extensive outwash blankets to the south. It is important to note that during this phase the major drainage from the ice sheet was to the south, and thus significant amounts of water and debris were transported through, and deposited in, the north-south valleys. In this area, the southern limit of the ice margin was approximately 15 kilometers north of the Village of Hamilton, at the approximate latitudes of Stockbridge Falls and Oriskany Falls. Outwash was deposited around and above stranded stagnant ice that remained to the south of the active ice margins. Subsequent melting of these ice masses gave rise to kettle depressions and kettle lakes rimmed by steep, angle of repose slopes. Such depressions often interrupt relatively flat outwash plain surfaces. 4. Modem Drainage Phase- As the ice margin withdrew from the present Mohawk River Valley and Oneida Lake Plain, drainage through the Mohawk and Hudson Rivers was established. (These rivers would have carried much greater discharges than at present, because the St. Lawrence River Valley was still ice-covered.) An abrupt decrease in the discharge of both sediment and water in the valleys of southern Madison County was the consequence of this newly-established drainage pattern. With the onset of essential present-day discharge, major transport and deposition of fluvial-glacial sediment ended, and minor incision and terracing of outwash plain surfaces ensued. The transition from Phase 2 to Phase 3 in the study area generally correlates with the "pre-Valley Heads" glaciation in the western Mohawk Valley (Ridge, Franzi and Muller, 1991). Valley Heads moraine deposition began approximately 15.5 ka. Glacial Sedimentary Facies: The surficial deposits of the study area can be broadly subdivided into sedimentary facies whose characteristics were controlled by the environments of deposition. These characteristics are briefly summarized below: 1. Lodgement Till: Surface exposures of lodgement tills are generally encountered un upland surfaces and the upper portions of valley walls. These materials were deposited beneath active ice as compact, poorly-sorted silt and clay-rich sediments. Angular, striated boulders are common, and such tills are dominated by locally-derived shale, siltstone and sandstone of the 252 Hamilton Group. Lodgement tills generally form thin veneers in areas of shallow bedrock on uplands, and are assumed to be present in the subsurface in lowlands. These tills have low hydraulic conductivity, and are therefore relatively poor aquifers. 2. Ablation Till: Ablation tills cover extensive areas of the uplands, and were deposited relatively passively during ice melt. These tills are often intercalated in complex fashion with fluvial-glacial deposits. Ablation tills are generally less compact and somewhat more well-sorted than lodgement till, although extreme ranges of particle size are characteristic. Locally derived lithologies dominate. 3. Ice-Contact Stratified Drift: Water-lain sands, gravels and silts deposited in contact with ice are common along lower valley walls and valley floors. These materials were deposited in subglacial, englacial, and proglacial streams within and adjacent to active ice margins, and in proximity to stagnant ice. Well-developed stratification and well-preserved primary sedimentary structures are typical, and post-depositional deformational features, such as soft-sediment folds and faults, are present. These sediments are generally moderately well-sorted, and form high quality aquifers. 4. Fluvial-glacial outwash: Well-sorted sands and gravels deposited by braided streams are the dominated surficial material in the valley floors. Pebbles and cobbles in these deposits are well rounded, and clast suites contain relatively high proportions of exotic lithologies. Outwash gravels are highly desirable aquifer materials, and are the source of good quality aggregate. 5. Proglaciallake and pond deposits: Proglaciallake delta deposits are often associated with ice-contact stratified and outwash facies. These deposits generally consist of well-sorted sand and gravel, with silts and clays comprising lake-bottom facies. Lake sediments are not abundant in the study area. The thickness of the glacial sedimentary cover is highly variable in the study area. On some upland ridges and on steeper valley walls, drift may be absent or but a few meters in thickness. In the valley floor areas, thickness of the total drift cover is commonly in excess of 40 meters. Soil Development and Surficial Geology: Postglacial soil development in southern Madison has been controlled by the typical factors of climate, slope, drainage vegetation and parent materials. In addition, clearing and tilling of land for agricultural purposes, which began in the early 19th century, has increased erosion rates, changed vegetative cover and altered near-surface portions of soil profiles. The great majority of soils are relatively well-buffered in the subsurface because of the abundance of carbonate minerals in the parent materials. However, as will be explored on this fieldtrip, acidic surface horizons are often present in areas of coniferous forest canopy, and, locally, in organic soils of swamp and marsh origin. Major soil orders: The dominant soils in the area are Alfisols and Inceptisols, with subordinate Entisols and Histisols. Alfisols are characterized by well-developed organic-rich surface horizons 253 (A-horizon) and relatively clay-rich B-horizons with significant enrichment of iron and aluminum. lnceptisols have less well-developed profile definition, and significant iron enrichment in the B horizon is absent. Entisols, which have relatively little profile development, are found on steeper slopes, areas of erosion and on modem stream floodplains where sedimentation occurs regularly. Histisols, which represent the accumulation of plant debris in areas with

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